Furnace runs but some rooms are too cold while others are too warm.

Safety first: Turn off power before adjusting internal furnace components.

• Filter and registers: Replace the filter and ensure all supply and return registers are open.
• Balance dampers: Adjust manual dampers in branch ducts (if present) to reduce airflow to overheated rooms and increase to colder rooms.
• Fan speed: A technician can adjust blower speed taps or ECM settings to better match the duct system.

Persistent imbalance may require duct modifications by an HVAC professional.